1. Field of the Invention
This invention relates to valves, and in particular to an emergency shut-off valve for use in swimming pools, spas and hot tubs and the like, to help prevent main drain entrapment.
2. Background of the Invention
Most people are aware of the possibility of drowning associated with water activities. Fences are erected around swimming pools in residential back yards to prevent non-swimming children from wandering into the pool. A less well-known hazard connected with swimming pools and hot tubs is the horrifying possibility of becoming entrapped by the vacuum pulled by the pool or hot tub pump at the main drain. If an individual--typically a child between the ages of 2 and 16--were to sit an a main drain, completely blocking it, disembowelment could occur. Even if the child were to block the main drain with a different body part, thus avoiding disembowelment, entrapment could occur, holding the child underwater. If the pump is not stopped, interrupting the vacuum, the child could drown.
A typical swimming pool main drain circulation system is depicted in FIG. 1. Pool 2 filled with water 4 comprises main drain 6 communicating with sump 9 covered by grate 8. Pump 12 draws water through outflow pipe 10 (the main drain "line") , and pumps it back into pool 2 through inflow pipe 14. A pool filter (not shown) is typically installed on inflow pipe 14 between pump 12 and pool 2. The pool circulation system is used to run pool water through the pool filter to clean water 4, as well as to provide a mixing effect to homogeneously distribute pool water additives such as chlorine, algaecide, acidity/alkalinity pH equalizers, etc.
Between the years 1980 and 1996 fifteen incidents of disembowelment were reported to the U.S. Consumer Product Safety Commission. See Guidelines for Entrapment Hazards: Making Pools and Spas Safer pg. 2 (U.S. Government Printing Office 1998). The typical scenario involved children between the ages of 2 and 6 who sit on the uncovered drain of a public wading pool whose cover has been broken or is missing. Id. When the child's buttocks cover the drain, evisceration can occur through the ruptured septum extremely quickly, even where the change of pressure is small. Id. A 2.2 pound vacuum is considered the threshold for evisceration. Pool and Spa News, pg. 22 (Apr. 23, 1997). The speed of the disembowelment in itself is frightening--the evidence indicates disembowelment injuries take place in a fraction of a second once the child sits on the drain. Pool & Spa News--Special Reports Pg. 7 (1997). Although the disembowelment is not generally fatal, the loss is permanent and irreversible, and has a devastating effect on the victim's future health and happiness. Guidelines for Entrapment Hazards: Making Pools and Spas Safer pg. 2 (U.S. Government Printing Office 1998).
Nine cases of body entrapment, including seven which resulted in death, were reported between January 1990 and May 1996. Id. Six of the incidents occurred in spas, two in swimming pools, and one in a wading pool. In one case, a sixteen year old girl was trapped on a 12 in..times.12 in. drain grate in a large public spa, and drowned. Id. These entrapment incidents involved primarily children between the ages of 8 and 16.
Still another entrapment scenario involves the victim's hair becoming entrapped in the main drain. At least 30 hair entrapment incidents were reported to the Consumer Product Safety Commission between 1990 and 1998, of which 10 were fatal. Id. at pg. 3. These incidents typically involved long, thin female head hair becoming entangled in the apertures and protrusions around main drain grates. The entrapment occurred because of entanglement, not strong suction forces. Id.
This main drain entrapment and disembowelment problem is viewed to be sufficiently serious to warrant legislative action: currently statutes exist in several states (including California and Ohio) requiring main drains safety features, and legislation is pending in several other states.
Existing Designs
A number of approaches have been taken towards preventing the disembowelment/entrapment problem. One approach has been to mandate at least two drains, so if one of them is obstructed, the other will operate to relieve excessive suction at the obstructed drain. Where only one drain has been installed in an existing pool or hot tub, this approach can be expensive, and may involve tearing up the existing concrete pool deck to install piping. In addition, independent valves for each resultant drain are typically provided. If one of the drain valves is closed, then the safety of the additional drain is defeated. Also, while two working drains may ameliorate the disembowelment problem and the suction entrapment problem, it does little to prevent the hair entrapment problem, which is not caused by suction.
Another approach has been to provide an indication and control system which senses a vacuum rise in the main drain line, and turns off the main drain pump, thus relieving the vacuum at the main drain after a certain time lapse. The presence of an indication and control system which includes a vacuum sensor attached to a switch, which then shuts down the main drain pump, which then after a period of time relieves the vacuum present at the main drain, necessarily involves a certain delay between the time the vacuum increases at the main drain and the time the vacuum is actually relieved at the main drain. If at any time during this inherent system delay the main drain vacuum exceeds the 2.2 pound threshold, permanent and irreversible damage has already been inflicted on the victim in the disembowelment scenario.
While the indication and control pump shut-off switch approach may help release individuals trapped by vacuum at the main drain before they drown, critics question whether these devices can prevent disembowelment, because disembowelment occurs so quickly, and it is difficult to determine exactly how much suction, and for what duration, the human body can tolerate vacuum without damage. See The Great Entrapment Debate, Pool & Spa News Pgs. 55, 56 (Aug. 18, 1999).
Although the currently available shut-off valves may prevent suction entrapments, they may be ineffectual in disembowelment accidents, because these occur in a fraction of a second. See Pool & Spa News--Special Reports Pg. 7 (1997).